Hydrofoils are well known as one means of supporting boats during travel across water to provide improved ride characteristics and decrease power requirements as compared to conventional hull boats. Heretofor several designs for the hydrofoil sections have been proposed for use in such applications. These designs were developed for application to aircraft propeller and wing sections for the express purpose of delaying compressability effect which were deemed detrimental to the aircraft's performance. Comparison of wind tunnel tests of the prior art hydrodynamic sections indicates that a significant improvement in lift-to-drag ratio at low Reynolds number is achieved by design wherein compressability effects are delayed. One of such hydrodynamic sections is known as NACA 16-XXX series which has been found to have the most desirable characteristics of the prior art hydrofoil sections including low supervelocity on the upper surface.
Some of the characteristics of the 16-XXX series are not desirable when considered from the standpoint of hydrodynamic application at full scale Reynolds numbers, namely the large negative pressure near the leading edge and the steep positive pressure gradient at the trailing edge which makes the section susceptable to flow variations including cavitation and boundary layer separation. The sensitivity of the flow to surface imperfections also can adversely effect the vehicle ride quality and operability. Aerodynamic sections proposed heretofor for usage in the environment where hydrofoils operate similarly do not offer the potential for significant improvement in operability and in ride quality.
Applications of hydrofoil systems to boats are well known in the art; however, heretofor the primary effort in the development of the technology has been toward establishing the control systems and methods of hydrofoil attachment, strut design, propulsion systems and the like. An example of a thorough treatment of such hydrofoil systems for boats appears in U.S. Pat. No. 3,465,704 to Baker wherein a hydrofoil system having control mechanisms and means to adjust the attitude and location of the hydrofoil elements is disclosed. This reference also provides helpful mathematical and computerized analysis of various components of the hydrofoil system. It is incorporated herein by reference for purposes of indicating the background of the invention and illustrating the state of the art.